So-called “replacement” intervertebral implants serve to replace one or two vertebral bodies together with their associated disks after one or two vertebrae have been removed in part. This type of implant is thus disposed between the vertebral bodies of two vertebrae. At each of its ends, the implant itself has a respective prosthetic plate for anchoring in an adjacent vertebral body, these vertebral plates usually being fitted with portions in relief firstly to provide effective anchoring of the prosthetic plates in the vertebral plates, and also to damage the plates in such a manner as to encourage bone growth within the implant itself.
Such a replacement implant is said to be “distractible” if the distance between the two prosthetic plates can be adjusted or adapted as a function of the spacing it is desired to achieve between the two vertebrae.
There exist numerous distractible intervertebral implants and they can be classified in two major categories. In the first category, there are distractible implants, which themselves include a mechanism enabling the distance between the prosthetic plates to be modified and adjusted. Those implants present the drawback of being relatively complex because of the presence of the mechanism for distracting the prosthetic plates.
In the second category, there are intervertebral implants that enable the distance between the prosthetic plates to be modified with the help of an external surgical instrument. Under such circumstances, the implant needs to have a mechanism that enables the distraction between the two plates to be maintained after the surgical distraction instrument has been removed.
In this second category, distractible intervertebral implants are known in which the prosthetic plates are mounted respectively at the ends of two cylinders that are themselves mounted telescopically. The two telescopic cylinders are prevented from moving relative to each other by known solutions using one or more cone-point screws.
It will be understood that such a system for interconnecting the cylinders on which the prosthetic plate are mounted present the drawback of not allowing the distance between the prosthetic plates to be adjusted continuously, since it is necessary to provide blind holes in the inside cylinder for receiving the cone-point screws, which are themselves mounted in the outside cylinder.
An object of the present invention is to provide a replacement intervertebral implant that is distractible in continuous manner, while presenting a structure that is mechanically simple.